Cut-out for electric instruments, glow-lamps, and the like.



A. J. DOWNES.

CUT-OUT FOR ELECTRIC INSTRUMENTS, GLOW LAMPS, AND THE LIKE APPLICATION FILED OCT. 11 I913.

Patented Feb.'27,1917.

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UNITED STATES PATENT oEEIoE.

ALLAN JOHN DOWNES, OF CROYDON, ENGLAND, ASSIGNOR OF ONE-HALF T0 JOHN VENNING, OF LONDON, ENGLAND.

CUT-OUT FOB ELECTRIC INSTRUMENTS, GLOW-LAMPS, AND THE LIKE.

Application filed October 11, 1913.

To all whom it may concern:

Be it known that I, ALLAN JOHN DowNEs, a subject of the King of England, residing in Croydon, Surrey, England have invented certain new and useful Improvements in Cut-Outs for Electrical Instruments, Glow- Lamps, and the like, of which the following is a specification.

This invention is for improvements in or relating to electrical instruments (which term is used to designate any device actuated by an electric current and provided with leads connected thereto, such devices comprising for example, incandescent electric lamps, electrical measuring instruments and the like), and has for its object to provide a by-pass for electric lamps which are to be burnt in series on the ordinary low pressure supply means, that is to say, at voltages below 250 volts across the parallel mains, and for a series arrangement say of 22 ten-volt lamps, and to provide a safety device for electrical instruments generally in low pressure circuits.

The term by-pass in this specification is used to designate means such as hereinafter described whereby two conductors are normally insulated from one another but are automatically brought into electrical connection when they are submitted to a difference of potential considerably higher than the normal.

The by-pass of the present invention relies upon an oxid whose electrical insulating properties are insufiicient to resist the igher pressure put upon it as a result of excess voltage in the line or the electric instrument with which it is in parallel becoming inoperative, but which although at such higher pressure it allows current to pass, does not have its insulating properties permanently destroyed by such passage.

The invention will now be described with reference to the accompanying drawings in which Figure 1 shows a lamp provided with a by-pass formed by twisting together the leading-in wires, and I Fig. 2 shows a lamp in which the by-pass comprises a ring slipped over the two leading-in wires.

Fig. 3 shows a lamp in which the by-pass comprises a number of metallic rings linked Specification of Letters Patent.

Patented Feb. 27, 1917.

Serial No. 794,720.

together to form a chain, the end rings being slipped over the leading-in wires.

Figs. 4 and 5 show enlarged views of bypasses comprising several oxid-coated metal rings.

Like reference characters indicate like parts in both the figures.

Referring to Fig. 1 the leading-in wires of the lamp, that is, the wires which are connected through the glass bulb A of the lamp to the filament B and to the cap C are usually made in three partsnickel D D inslde the bulb, platinum E E passing through the bulb, and copper or like metal F F between the bulb and the cap.

In manufacturing a lamp according to the present invent-ion the wires F F are first heated in air so that an oxid of'the metal forming the wires is formed as a coating thereon, and they are then twisted together as shown at G. It is found convenient to give the wires two complete turns. If, as is usual, the wires F F are of copper the thin coating produced by heating the wires appears to be black cupric oxid. The cap is thereafter fitted in the ordinary way.

Fig. 2 shows a modification of the invention in which the wires F F are not heated or twisted together, but are formed in the usual way. A small metallic ring H, say of copper, is heated so as to give it a coating of an oxid of the metal of which it is made, and this ring is slipped over the two wires F F so as to contact with both. Each of the wires F F is thus separated from the ring H by the film of oxid. Otherwise the lamp is made up in the usual way.

One convenient method of making oxicontact. Thus a single contact may break down on the application of between 30 to 100 volts, while two or more such contacts can sustain a considerably higher voltage. According therefore to the present nvention when a lamp or other electrical instrument is normally operating at a pressureof say 100 volts or upward, two or more insulating contacts as required may be employed. For example two or more oxidlzed metal rings may be linked together, and the leading-in wires would be arranged to keep the linkage taut.

Fig. 3 shows an electric lamp in which the by-pass is formed of a number of ox1dcoated metallic rings H linked together to form a chain, the end rings being slipped over the leading-in wires F F The chain may be kept taut by a plug, such as a cork J, inserted in the lower end of the lamp.

Fig. 4c shows an enlarged view of the leading-in wires of an electric lamp provided with a by-pass formed of a chain of oxid-coated rings H, and in which the leading-in wires F F are twisted to form loops K K through which the end rings of the chain pass.

Fig. 5 shows an enlarged view of the leading-in wires of an electric lamp provided with a by-pass formed of two oxid-coated rings H linked together, one ring being slipped over one leading-in wire, and the other over the second leading-in wire.

llt is to be understood that although the ring has been described as oxidized, the leading-in wires may be oxidized.

Taking as an example of the application of the invention a case in which ten QO-volt lamps are burning in series on a QOO-volt circuit, the insulation between the two leading-in wires due to the film of oxid is sufficient normally to prevent current flowing between these wires, so that the current passes through the lamps and causes them to glow. Should the filament of a lamp become broken, the passage of current through the lamp is interrupted, and the leading-in wires are immediately subjected to the full pressure of the circuit, that is 200 volts. This abnormally high difference of potential causes current to pass between the leading-in wires across the film of oxid, so that the remaining nine lamps of the circuit continue to burn. It will be appreciated that the inoperative lamp should be replaced as soon as possible as the remaining lamps will be somewhat over-run.

At present telegraph instruments are protected from accidental excess voltage (caused for example by the falling of a power circuit wire on the telegraph wire) by various thermal safety devices, having more or less time lag. When aby-pass according to the present invention is applied to a telegraph or other instrument, the said instrument is provided with two wires connected to its terminals, and the wires themselves are insulated from one another by any one of the forms of by-pass hereinbefore described. For example the two wires might be oxidized and twisted together, or they might be oxidized and connected by a metal ring, or an oxidized metal ring could be slipped over unoxidized wires. On the application of excess voltage the instrument is instantaneously short-circuited. lVhen the voltage returns to normal the by-pass can be made effective again by merely tapping it, for the passage of current does not permanently destroy its insulating properties. This is particularly useful in the case of measuring, telegraph or like instruments, since there is no necessity to renew the by-pass after each time it has acted to protect the instrument from excess voltage.

It will be appreciated that the by-pass of the present invention is much less complicated than by-passes in use, and is exceedingly simple to manufacture; moreover it can. be manufactured as a separate device as already described in connection with instruments, and may be used many times.

What I claim as my invention and desire to secure by Letters Patent is I 1. The combination of an electric instrument for use on low pressure circuits, electric leads connected thereto, and a by-pass in parallel therewith, said by-pass being located in an oxidizing atmosphere and comprising a film of oxid connecting the leads but normally insulating one lead from the other.

2. The combination of an electric instrument for use on low pressure circuits, electric leads connected thereto, and a by-pass in parallel therewith, said by-pass being located in an oxidizing atmosphere and comprising an electric conductor connecting the leads, one of the members being oxidized, so that the leads are normally insulated one from another by a film of oxid.

3. The combination of an electric instrument for use on low pressure circuits, electric leads connected thereto, and a by-pass in parallel therewith, said by-pass being lo cated in an oxidizing atmosphere and comprising an oxidized link connecting the two leads to each other, the oxidized film on the link normally insulating one lead from the other.

4. The combination of an incandescent electric lamp for series lighting on low pressure circuits, of a bypass in parallel therewith, said by-pass being located outside of the exhausted lamp bulb and comprising a film of oxid connecting the two metallic conductors for the lamp but normally insulating one conductor from the other.

5. The combination of an electric instrument for use on low pressure circuits, electric leads connected thereto, and a by-pass in parallel therewith, said by-pass being located in an oxidizing atmosphere and comprising a film of copper oxid connecting two conductors but normally insulating one conductor from the other.

6. The combination of an incandescent In testimony whereof I have signed my electric lamp for series lighting on low presname to this specification in the presence of 10 sure circuits, of a by-pass in parallel Ctheretwo subscribing Witnesses. with, said by-passbeing located outsi e the 5 exhausted lamp bulb and comprising a film ALLAN JOHN DOWNES' of copper oXid connecting two conductors Witnesses: but normally insulating one conductor from HARRY S. MIDGE, the other. PERCY HEWI'I'I. 

